1. Field of the Invention
The present invention relates to a gas laser oscillator, and in particular relates to a as laser oscillator having auxiliary electrodes.
2. Description of Related Art
Gas laser oscillators including a laser power supply that can output high frequency powers having a phase difference of 180 degrees to two laser gas circulation paths are known (for example, Japanese Unexamined Patent Publication (Kokai) No. S60-161687 hereinafter referred to as “patent document 1”, and Japanese Unexamined Patent Publication (Kokai) No. 2013-247261 hereinafter referred to as “patent document 2”). The gas laser oscillators include a matching unit constituting coils and capacitors to be used for impedance matching with discharge loads (discharge tubes, auxiliary electrodes, and a laser gas), in other words, to produce resonance so as to maximize discharge tube voltages. The laser power supply supplies the high frequency powers to a plurality of discharge tubes and auxiliary electrodes through the matching unit.
To start a discharge (main discharge) of the discharge tube, a discharge (auxiliary discharge) of the auxiliary electrode is required to have already been started. Increasing the output of the laser power supply, in a state of not starting the auxiliary discharge, causes an excessive voltage to be applied to the discharge tube and an excessive current to flow through the laser power supply, thus resulting in a break in each of the discharge tube and the laser power supply or a stop of the gas laser oscillator while issuing an alarm.
The patent document 1 discloses a technique in which auxiliary electrodes are provided upstream of discharge tubes through which a laser gas circulates. Electrons are supplied by an auxiliary discharge, before starting a main discharge, to ensure that the main discharge is stably started. However, this technique requires as many auxiliary electrodes as the number of the discharge tubes, thus causing a difficulty in cost reduction.
The patent document 2 discloses a technique in which through-holes are provided in discharge tubes, and a main discharge is stabilized by increasing the number of auxiliary electrodes. However, this technique requires, as well as an increase in cost of the discharge tubes themselves, an exchange of the expensive discharge tubes and the auxiliary electrodes on a regular basis. Furthermore, this technique increases the risk of bringing serious leakage problems such as a reduction in a laser power and a break in the discharge tube owing to an arc discharge, in the event that a laser gas leaks from portions (O-rings) of the auxiliary electrodes.
As described above, the conventional art has a problem that as many auxiliary electrodes as the number of discharge tubes are required to ensure that a main discharge is stably started.